[Hibernate] Open Session in View Pattern
I get this question a lot when folks check out my struts-resume application - so I figured I'd document it here - and then I can just send future developers a URL. The question is this:
Why do you tie your View to your Model Implementation by putting a Hibernate Session in your Service Interfaces?
I have a couple of reasons. The first reason is that I initially had ses.currentSession() and ses.closeSession() at the beginning and end of each DAO
method. In fact, I found this old
e-mail where you can see an example. This seemed to work for me and
I was happy with it. However, I got an e-mail from Gavin
(Hibernate's Lead Developer) that I was doing it all wrong. He said that I
should use one session per request, rather than one on each method. Why? For
performance reasons and to allow rolling back the entire session, rather
than just a method. At least that's why I remember him saying.
So I refactored and implemented the Open Session in View pattern
in conjunction with the Thread Local Session. You
can checkout my ActionFilter and ServiceLocator for the View and
ThreadLocal, respectively.
The problem now is that I pass my the Session object from my View ->
Business Layer [example: UserManager]
-> DAO Layer. So I'm tightly coupled with Hibernate, which I don't mind,
because I really, really like Hibernate and have no plans to
implement an alternate DAO (even though the architecture allows it). Even
if I did choose to implement a new plain ol' JDBC DAO Layer, I can always
get a java.sql.Connection from the Session using
ses.connection(). Another option I've thought of is to just
pass the ServiceLocator between the different layers, and call
ses.currentSession() or ses.connection() when it's
needed. But that seems to be the same thing I was doing before when I was
opening/closing at the method level.
Comments and suggestions, as always,
are welcomed and encouraged.